The effectiveness with which democratic societies respond to climate change depends on how well the problem is understood by the lay public. Citizens must decide which public policies to support, and whether and how to consider ecological implications when making personal consumption choices. Survey research can reveal where citizen knowledge is lacking, but is less effective at predicting how individuals will incorporate new information into pre-existing knowledge and belief structures, i.e., mental models. In this study we used a mental models approach to characterize public understanding of climate change in the Pacific Northwest of the United States.

The results of 56 open-ended interviews in 2008 suggest that respondents regarded climate change as both negative and very likely. Furthermore, when comparing our 2008 interview responses with similar interview data from 1992, we find that our 2008 respondents demonstrated many increases in basic familiarity with the causes and consequences of climate change. A slim majority of 2008 respondents (51%) correctly cited fossil fuel use as a cause of climate change, and nearly a third cited carbon dioxide specifically (20% mentioned both). In other areas, however, improvements in comprehension of climate processes and impacts was less evident. For example, "pollution" was the most frequently mentioned cause of climate change in 2008 (cited by 60% of respondents), although when asked to specify what kinds of pollution they were thinking about responses ranged from highly relevant climate change causes (e.g., coal and oil burning) to largely irrelevant forms of pollution (e.g., littering).

Overall our interviews suggest that though comprehension of some issues has improved, mental models of climate change processes in the 21st Century still exhibit several of the same idiosyncrasies observed in mental models of climate change in the early 1990s. Even in 2008 our respondents nominated ozone depletion as a cause of climate change almost as frequently as carbon dioxide emissions (and more frequently than other greenhouse gas emissions). Furthermore, while industrialization in developing countries was correctly cited as another cause, domestic electricity use in the U.S. was volunteered by very few. Finally, although many respondents cited “natural processes” as a major contributor to climate change (and over two-thirds mentioned ecosystem impacts as a result of climate change), concepts such as feedback loops and ecological thresholds were almost entirely absent from people's mental models.

The specter of global climate change has brought the issue of climate change to the forefront of scientific and political debates. But to have practical value, some shared understandings of core climate change concepts must make their way to all decision makers, including individual citizens. Investigating how laypeople think about climate change and how they process new information will strengthen such communications efforts.